Signal analyzer and method for displaying power levels of code channels with orthogonal transmit diversity

ABSTRACT

A signal analyzer and a method for displaying power levels of code channels of a CMDA signal sent with orthogonal transmit diversity (OTD) via at least one of at least two antennae is described. Once a code class has been determined for representing the power of each individual code channel, the power levels of the code channels in the next highest code class are defined and associated with a respective antenna. Once a code channel exchange has been carried out according to the actual association of the antennae in relation to the code class of the actually active code channels, the power levels of the code channels for at least one antenna are correctly represented on a display device in terms of the antenna.

FIELD OF THE INVENTION

The invention relates to a signal analyzer and also to a method fordisplaying power levels of code channels of a CDMA (Code DivisionMultiple Access) signal.

BACKGROUND OF THE INVENTION

In order to check components for third-generation mobile radio systems,it is necessary to determine power levels of individual code channels ofwhich the whole signal is composed. In order to implement an evaluationof the measured power levels of the individual code channels, therespective power levels of the code channels are representedgraphically.

For this purpose, it is known from U.S. Pat. No. 6,219,340 B1 torepresent the individual power levels of the code channels in the formof a bar. The individual code channels are plotted in the direction ofthe X axis such that the code channels associated respectively with onecode class are disposed situated one next to the other. The length ofthe bars represented for each code channel in the Y direction therebyindicates the measured power level of the respective code channel. Theassociation of the individual code channels with one code class, i.e.with a specific spreading factor (SF), is achieved in the proposedrepresentation in that, corresponding to the lower spreading factor ofthe lower code class, the representation of the assigned bars for therespectively corresponding code channel of the lower code class iswider.

In the evaluation of signals with orthogonal transmit diversity, theproblem exists that the power levels of the individual code channels andtheir distribution to the antennae used are thus not detectable. Inparticular, it is not provided to represent those code channels, whichare associated with an active antenna of an actually active codechannel, en masse.

The disadvantage is produced therefrom that, for an antenna withorthogonal transmit diversity (transmission via a plurality of antennaewith a code which is orthogonal for the antennae), only a part of thepower levels of code channels which are actually relevant for an activecode channel is represented.

SUMMARY OF THE INVENTION

There exists a need to produce a signal analyzer and also a method fordisplaying power levels of code channels, in which, for CDMA signalswith transmit diversity, the power levels of the code channels to berepresented for respectively one antenna are represented completely.

With orthogonal transmit diversity, the signal of an active code channelis distributed to at least two antennae. For this purpose, twoorthogonal codes are generated which can be taken from the next highercode class. The lower code channel number is then assigned to antenna 1,the higher code channel number to antenna 2.

Because of generating the individual codes of the code channels for therespective code classes and because of the specification for transmitdiversity that the respectively lower code channels, i.e. those codechannels with the lower code channel numbers, must be assigned to afirst antenna or respectively the upper code channels to a secondantenna when a signal is transmitted with transmit diversity, only everysecond measured code channel is assigned to the code branch of theactually active antenna in the representation of an active code channelin a higher code class. This misleading assignment is corrected by themethod according to the invention or respectively in an evaluationdevice of the signal analyzer according to the invention correspondingto the production of the code channels from the Hadamard matrix. Hencein the corrected representation, the power levels of all code channelsassociated respectively with an actually active antenna are displayed.

Still other aspects, features, and advantages of the present inventionare readily apparent from the following detailed description, simply byillustrating a number of particular embodiments and implementations,including the best mode contemplated for carrying out the presentinvention. The present invention is also capable of other and differentembodiments, and its several details can be modified in various obviousrespects, all without departing from the spirit and scope of the presentinvention. Accordingly, the drawing and description are to be regardedas illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is represented in the drawing and is explained in moredetail by means of the subsequent description with reference toembodiments. There are shown:

FIG. 1 a schematic representation of a section of a code tree;

FIG. 2 an overview of the assignment for the example from FIG. 1;

FIG. 3 a block diagram of a measuring system, given by way of example,with the signal analyzer according to the invention;

FIG. 4 a further schematic representation of a section of a code tree;

FIG. 5A-C three further schematic representations of sections of a codetree;

FIG. 6 a graphic representation of the display device beforeimplementation of the code channel exchange; and

FIG. 7 a graphic representation of the power levels of the code channelsafter implementation of the code channel exchange.

In FIG. 1 a section of a code tree is represented schematically. Theindividual code classes are plotted in the horizontal direction, whichcode classes are designated with the references CC5 for code class 5,CC6 for code class 6 etc. In the represented example, the code channelwith the number 19 of the code class CC5 is intended to be active. Upontransmission of the signal with orthogonal transmit diversity, the codeassigned to the code channel 19 of the code class CC5 is spread by anadditional factor for distribution to the two antennae Ant1 and Ant2.The channel 19, which is actually active in code class CC5 is thereforetransmitted in the code class CC6 as code channel 19 to antenna Ant1 andas code channel 51 to antenna Ant2.

The law for forming code channel numbers is as follows: the code channelnumber for antenna Ant1 is the base code channel number. The codechannel number for antenna Ant2 is the base code channel number plus thebase spreading factor.

It may be assumed in the present example that a representation of thepower levels of the code channels in code class CC7 is intended to beeffected. For this purpose, it is firstly required to take into accountthe additional spreading factor on the basis of the orthogonal transmitdiversity, the next higher code class CC8 being measured before therepresentation of the code class CC7. In accordance with thespecification for generating the codes and assigning the code channelsto the individual antennae with the orthogonal transmit diversity, theindividual code channels, as represented in FIG. 1, are distributed tothe antenna Ant1 or respectively antenna Ant2.

This means that measurement of the power levels of the individual codechannels is produced in the code class CC8, that the power levels of thecode channels 19, 83, 51 and 115 are measured for the antenna Ant1 and,for the antenna Ant2, the code channels 147, 211, 179 and 243. Thisassignment is produced from the specification that respectively thelower half of the channel numbers must be assigned to the antenna Ant1and the upper half of the channel numbers to the antenna Ant2.

For the chosen example, the antenna Ant1 with the code channel 19 incode class CC5 is however actually active so that the code channels 19,147, 83 and 211 must be assigned to the antenna Ant1 for correctantenna-wise reproduction of the measured power levels, as is producedfrom the representation of the corresponding code branch in FIG. 1 whichcorresponds to a “bit-reverse representation”. Therefore, a correctantenna-wise representation comprises for antenna Ant2 the code channels51, 179, 115 and 243 which are produced from the code branch which hasits origin in code class CC6 in the code channel 51.

In FIG. 2, the assignment for the chosen example from FIG. 1 isrepresented schematically. In the upper half of FIG. 2, the power levelsof the code channels are represented just as they are produced directlyfrom the measurement in code class CC8. This leads to the fact that thecode channels with the numbers 19, 51, 83 and 115 which are present incode class CC7 are represented respectively once for antenna Ant1 andare represented once for antenna Ant2 because of the orthogonal transmitdiversity. For antenna Ant2, in addition the code channel number, as isrepresented in code class CC8 of FIG. 1, is plotted for bettercomprehension.

As was cited already with respect to FIG. 1, a correctly assignedrepresentation of the antenna Ant1 in code class CC7 would have tocomprise those code channels which were generated from the code channel19 of the code class CC6 corresponding to the code branch. In the upperhalf of FIG. 2, these code channels are represented by the bars whichare not filled in.

In order now to enforce a correct antenna-wise assignment of the codechannels, the code channels associated respectively with the antennaAnt1, as is represented by the arrows in FIG. 2, are assigned accordingto the invention actually to the antenna Ant1. The code channelsrepresented in grey in the upper half of FIG. 2, which code channelsshould actually be assigned to the antenna Ant2, are representedcorrectly according to the invention correspondingly in the lower halfon the right in the case of antenna Ant2.

In order that no power level values of the code channels are overwrittenin the implementation of the correct assignments, prior to theimplementation of the representation of the individual code channelswith respect to their respectively actually active antenna, a copy ofthe measurement result is produced. Hence all the power levels of thecode channels are maintained with their correct value.

The representation with respect to the actual active antenna of anactive channel is of particular advantage when transmission does nottake place via both antennae but only one of the two antennae is active.As can be detected directly from the upper half of the representation inFIG. 2, without the implementation of the correct assignment, both theantenna Ant1 and the antenna Ant2 would have channels with power. Afterimplementation of the code channel exchange, there is displayed for anactually active antenna Ant1 in the lower half only power for codechannels which are actually assigned to the antenna Ant1, whereas nopower would be displayed for the code channels of the antenna Ant2 whichare represented in grey.

A block diagram is represented in FIG. 3, which shows a signal analyzer1 according to the invention, by means of which for example the signalof a base station 2 is intended to be analysed. The signal analyzer 1comprises an evaluation device 3 and a display device 4. A CDMA signal 5is supplied via an input connection 6 to the signal analyzer 1. In therepresented embodiment, the CDMA signal 5 is received via a change-overswitch 8 which is connected to the signal analyzer 1. Instead of thedirect connection line, via which the signal 5 is transmitted, also anantenna could be connected to the input connection 6 which receives theCDMA signal 5 beamed from the base station 2 via the antennae Ant1,Ant2, or a combiner, which generates the total signal of antenna Ant1and antenna Ant2.

After the CDMA signal 5 of only one of the two antennae Ant1 or Ant2 isreceived by the signal analyzer 1, the power level for the code channelsof that code class which is the next higher code class to the one to berepresented, is determined in the evaluation device 3, which code classis established for example by an operator. In the above-describedexample, that would be the code class CC8 for the code class CC7 to berepresented. Subsequently, a representation of the measured powers ofthe code channels is generated in the evaluation device 3, finally thecode channels, which must be assigned to the corresponding antenna Ant1or respectively antenna Ant2, being determined from this representation.

The thus determined powers of the code channels for the antenna Ant1 orrespectively for the antenna Ant2 are subsequently supplied via aconnection 9 to the display device 4. On the display device 4, a bardiagram is then preferably represented which contains the power levelsof the code channels for the code class to be represented, in thepresent case the code class CC7, the display device 4 preferablyrepresenting respectively only antenna Ant1 or antenna Ant2.

In FIG. 4, the resultant code tree for an active code channel 2 of thecode class 2 is represented. Because of the orthogonal transmitdiversity, the active code channel 2 of the code class CC2 istransmitted via an antenna Ant1 and an antenna Ant2, the antenna Ant1containing the code channel 2 of the code class CC3 and the antenna 2the code channel 6 of the code class CC3. In a representation of themeasured power level of the individual code channels, there shouldtherefore be displayed, for the antenna Ant1, respectively that powerlevel of the code channels which emanate from the code channel 2 of thecode class CC3. In FIG. 4, this is the entire upper half of therepresented code tree. If a representation of the code class CC6 ischosen, the code channels 2, 66, 34 etc. up to 122 would therefore haveto be correspondingly represented in a correct antenna-wiserepresentation with respect to the antenna Ant1, as this corresponds tothe upper half of the code channels represented with respect to codeclass CC7.

For representation of the power levels of the code channels in codeclass CC6, the power level of the individual code channels in the codeclass CC7 must be measured with orthogonal transmit diversity, as hasbeen described above already. Because of the assignment of theindividual code channel numbers to antenna Ant1 or respectively Ant2, itis thereby revealed that only every second code channel number of thecode class CC7 is assigned to the antenna Ant1.

For representation of the power level on the display device 4, thechannels are sorted according to the invention such that increasing codechannel numbers are disposed on the X axis. In code class CC7, thechannel numbers 0 to 127 exist, the code channel numbers 0 to 63 beingassigned to the antenna Ant1 and the code channel numbers 64 to 127 toantenna Ant2. The representation resulting therefrom on the displaydevice 4 of the signal analyzer 1 is represented in FIG. 6, it beingassumed that respectively only noise power level is measurable for theantenna Ant2. Without implementation of the code channel exchangeaccording to the invention, a power level of an active code channel istherefore measurable only for the code channels 2, 10, 18, 26, 34, 42,50 and 58 which are represented in a dark colour in FIG. 6.

It is revealed in contrast from the code branch of the antenna Ant1 ofFIG. 4 that power levels, which are measurable in the code channels 66,74, 82, 90 etc., should likewise be assigned to the antenna Ant1.

After implementation of the code channel exchange according to theinvention, the image represented in FIG. 7 is produced on the displaydevice 4, the code channels 66, 74, 82 etc. assigned originally to theantenna Ant2 having now been represented in the region of the lower codechannel numbers and hence being correctly represented antenna-wise forthe antenna Ant1. In FIG. 7, power levels for the code channels 2, 6,10, 14, 18, 22, 26 etc. can therefore be detected.

In FIGS. 5A, 5B and 5C, further sections of code trees for the activecode channel 3 of the code class CC3, the active code channel 15 of thecode class CC4 and the active code channel 20 of the code class CC5 arerepresented. The power levels measured respectively in the code classCC7 for antenna Ant1 are, corresponding to the example from FIG. 4explained above in detail, likewise represented in FIG. 6. For betterdifferentiation, the thus represented code channels 3, 15, 19, 20 etc.are represented in light grey.

In contrast, FIG. 7 shows in turn a correct antenna-wise representationof all the power levels in the code channels measured with respect toone antenna Ant1. For the sake of a more comprehensible representation,it was assumed in the representation of FIG. 6 that the antenna Ant2respectively is inactive. In practice however, generally also antennaAnt2 will contribute to the data transmission. In order that the powerlevel of the antenna Ant2 occurring in the respective code channels isnot overwritten by the power levels of the antenna Ant1 in the codechannel exchange, a corresponding storage of the power levels comingfrom antenna Ant2 is required in advance. Such a storage can be achievedfor example by copying the power levels of the individual code channels,before implementation of the code exchange, into a memory.

1. A method for displaying power levels of code channels of a CDMA (CodeDivision Multiple Access) signal, which is transmitted with orthogonaltransmit diversity (OTD), the signal being transmitted via at last oneof at least two antennae, having the following method steps: receivingthe CDMA signal determining a code class for the representation of thepower level of the individual code channels; determining the powerlevels of the individual code channels in the next higher code classwith respect to the determined code class; assigning the powers of theindividual code channels to the respective antenna corresponding to theorthogonal transmit diversity in the determined code class; implementinga code channel exchange corresponding to the actual assignment of theantennae with respect to the code classes of the actually active codechannels; and displaying the power levels of the exchanged code channelsfor at least one antenna.
 2. A method according to claim 1, wherein:displaying the power levels of the actually active code channels inconjunction with the power levels of the code branches associated withthe respective active code channels.
 3. A signal analyzer for analyzingCDMA signals with orthogonal transmit diversity for at least twoantennae, the CDMA signal being transmitted via at least one of at leasttwo antennae, comprising: an evaluation device configured for detectingthe power levels of respective code channels and assigning the codechannels, which are detected with respect to a corresponding code classto be represented in the next higher code class and distributedcorresponding to the orthogonal transmit diversity to the respectiveantennae, respectively to said respective antennae which is actuallyactive on the basis of the orthogonal transmit diversity with respect tothe active code channel, and a display device configured for displayingthe power levels of the code channels assigned to the antennae by theevaluation device.
 4. A signal analyzer according to claim 3, whereinthe display device represents the powers of the code channels forrespectively only one actually active antenna.
 5. A signal analyzeraccording to claim 3, wherein the display device represents the powersof active code channels as a sum of the powers of the individual codebranches.